Isoprenylcysteine carboxylmethyltransferase is associated with nasopharyngeal carcinoma chemoresistance and Ras activation

Inhibition of mitochondrial function by approved drugs overcomes nasopharyngeal carcinoma chemoresistance

The development of chemo-resistance in nasopharyngeal carcinoma (NPC) presents a significant therapeutic challenge, and its underlying mechanisms remain poorly understood. In our previous studies, we highlighted the association between isoprenylcysteine carboxylmethyltransferase (ICMT) and chemoresistance in NPC. In this current research, we revealed that both 5-FU and cisplatin-resistant NPC cells exhibited elevated mitochondrial function and increased expression of mitochondrial genes, independent of ICMT. Our investigations further showed that classic mitochondrial inhibitors, such as oligomycin, antimycin, and rotenone, were notably more effective in reducing viability in chemo-resistant NPC cells compared to parental cells. Moreover, we identified two antimicrobial drugs, tigecycline and atovaquone, recognized as mitochondrial inhibitors, as potent agents for decreasing chemo-resistant NPC cells by targeting mitochondrial respiration. Remarkably, tigecycline and atovaquone, administered at tolerable doses, inhibited chemo-resistant NPC growth in mouse models and extended overall survival rates. This work unveils the efficacy of mitochondrial inhibition as a promising strategy to overcome chemo-resistance in NPC. Additionally, our findings highlight the potential repurposing of clinically available drugs like tigecycline and atovaquone for treating NPC patients who develop chemoresistance.

ZNF24 regulates the progression of KRAS mutant lung adenocarcinoma by promoting SLC7A5 translation

Background

Clinical treatment of RAS mutant cancers is challenging because of the complexity of the Ras signaling pathway. SLC7A5 is a newly discovered downstream gene of the Ras signaling pathway, but the regulatory mechanism is unclear. We aimed to explore the molecular mechanism and role in KRAS mutant lung adenocarcinoma progression.

Methods

Key gene that regulated SLC7A5 in KRAS mutant lung adenocarcinoma was screened by RNA sequencing and bioinformatics analysis. The effect of this gene on the expression of SLC7A5 was studied by RNAi. The regulatory mechanism between the two genes was investigated by immunofluorescence, CoIP, pulldown and yeast two-hybrid assays. The location of the two genes was determined by inhibiting Ras and the downstream pathways PI3K-AKT and MEK-ERK. By in vivo and in vitro experiments, the effects of the key gene on the biological functions of KRAS mutant lung adenocarcinoma were explored.

Results

We found a novel gene, ZNF24, which upregulated SLC7A5 protein expression rather than mRNA expression in KRAS mutant lung adenocarcinoma. Endogenous protein interactions occurred between ZNF24 and SLC7A5. Ras inhibition reduced the expression of ZNF24 and SLC7A5. ZNF24 and SLC7A5 are located downstream of the MEK-ERK and PI3K-AKT pathways. In vivo and in vitro functional experiments confirmed that the ZNF24-SLC7A5 signaling axis promoted the proliferation, invasion and migration of KRAS mutant lung adenocarcinoma.

Conclusions

ZNF24 promoted the growth of KRAS mutant lung adenocarcinoma by upregulating SLC7A5 protein expression, which suggested that ZNF24 is a new biomarker of KRAS mutant tumors and could be a new potential therapeutic target for Ras-driven tumors.

Protein Farnesylation on Nasopharyngeal Carcinoma, Molecular Background and Its Potential as a Therapeutic Target

Simple Summary

Nasopharyngeal carcinoma is distinguished from other head and neck carcinomas by the association of its carcinogenesis with the Epstein–Barr virus. It is highly metastatic, and a novel therapeutic modality for metastatic nasopharyngeal carcinoma is keenly awaited. Protein farnesylation is a C-terminal lipid modification of proteins and was initially investigated as a key process in activating the RAS oncoprotein through its association with the cellular membrane structure. Since then, more and more evidence has accumulated to indicate that proteins other than RAS are also farnesylated and have significant roles in carcinogenesis. This review delineates molecular pathogenesis through protein farnesylation in the context of nasopharyngeal carcinoma and discusses the potential of farnesylation as a therapeutic target.

Abstract

Nasopharyngeal carcinoma (NPC) is one of the Epstein–Barr virus (EBV)-associated malignancies. NPC is highly metastatic compared to other head and neck carcinomas, and evidence has shown that the metastatic features of NPC are involved in EBV infection. The prognosis of advanced cases, especially those with distant metastasis, is still poor despite advancements in molecular research and its application to clinical settings. Thus, further advancement in basic and clinical research that may lead to novel therapeutic modalities is needed. Farnesylation is a lipid modification in the C-terminus of proteins. It enables proteins to attach to the lipid bilayer structure of cellular membranes. Farnesylation was initially identified as a key process of membrane association and activation of the RAS oncoprotein. Farnesylation is thus expected to be an ideal therapeutic target in anti-RAS therapy. Additionally, more and more molecular evidence has been reported, showing that proteins other than RAS are also farnesylated and have significant roles in cancer progression. However, although several clinical trials have been conducted in cancers with high rates of ras gene mutation, such as pancreatic carcinomas, the results were less favorable than anticipated. In contrast, favorable outcomes were reported in the results of a phase II trial on head and neck carcinoma. In this review, we provide an overview of the molecular pathogenesis of NPC in terms of the process of farnesylation and discuss the potential of anti-farnesylation therapy in the treatment of NPC.

Isoprenylcysteine carboxyl methyltransferase is critical for glioblastoma growth and survival by activating Ras/Raf/Mek/Erk

PURPOSE

The poor outcomes in glioblastoma necessitate new therapeutic target. Isoprenylcysteine carboxyl methyltransferase (ICMT), a unique enzyme of the final step of prenylation that modifies activities of oncogenic proteins, represents a promising target for many cancers.

METHODS

Expression pattern, function and downstream pathway of ICMT in glioblastoma were analyzed using immunohistochemistry, ELISA, cellular assays and immunoblotting method. Combinatory effect was analyzed using Chou-Talalay approach.

RESULTS

Upregulation of ICMT expression is a common phenomenon in glioblastoma patients regardless of clinicopathological characteristics. Gain-of-function and loss-of-function analysis support the role of ICMT in glioblastoma growth and survival but not migration. Importantly, pharmacological inhibitors of ICMT are effectively against glioblastoma cells while sparing normal neuron cells, and furthermore that they act synergistically with chemotherapeutic drugs. Consistently, ICMT inhibitor UCM-1336 significantly inhibits glioblastoma growth without causing toxicity in mice. Mechanistic studies demonstrate that Ras/Raf/Mek/Erk rather than Ras/PI3K/Akt/mTOR is the downstream pathway of ICMT-mediated glioblastoma growth.

CONCLUSIONS

Our findings provide the proof-of-concept of pharmacologically targeting ICMT in the treatment of glioblastoma via deactivation of Ras/Raf/Mek/Erk.

BarH-like homeobox 2 represses the transcription of keratin 16 and affects Ras signaling pathway to suppress nasopharyngeal carcinoma progression

Nasopharyngeal carcinoma (NPC) refers to a malignancy initiating from the superior mucosal epithelium of the nasopharynx. Optimal therapies for NPC are still needed. In this investigation, we attempted to explore whether BarH-like homeobox 2 (BARX2), a well-known tumor suppressor, had anti-cancer properties on NPC, and the possible mechanisms. After searching for NPC-related databases, we determined BARX2 as one of the core genes in NPC. The results of RT-qPCR and immunohistochemistry or Western blot demonstrated that BARX2 was reduced in NPC patients and cells. Ectopic expression of BARX2 reverted the malignant phenotype of NPC cells. Mechanistically, BARX2 bound to the keratin 16 (KRT16) promoter to downregulate its expression. In addition, BARX2 was found to reduce the phosphorylation levels of MEK and ERK. Further KRT16 upregulation in cells overexpressing BARX2 promoted malignant aggressiveness of C666-1 and HNE3 cells and activated the Ras signaling pathway. BARX2 inhibited the growth and metastasis of tumors and suppressed the Ras signaling pathway in vivo. In conclusion, our findings indicate that BARX2 reverts malignant phenotypes of NPC cells by downregulating KRT16 in a Ras-dependent fashion. BARX2 might act as a possible therapeutic regulator for NPC.

Investigations on the Role of the MicroRNA-338-5p/Wnt Family Member 2B (WNT2B) Axis in Regulating the Pathogenesis of Nasopharyngeal Carcinoma (NPC)

Background

The involvement of microRNA-338-5p in modulating NPC pathogenesis is still largely unknown, and this study aimed to investigate this issue.

Methods

The expressions of cancer associated genes were determined by Real-Time qPCR and Western Blot, and cell apoptosis was determined by flow cytometer (FCM). CCK-8 assay and colony formation assay were respectively used to determine cell proliferation and colony formation abilities. Transwell assay was used to evaluate cell migration. The expression levels of Ki67 protein in mice tissues were measured by Immunohistochemistry (IHC) assay.

Results

The present study found that microRNA-338-5p suppressed NPC progression by degrading its downstream target, Wnt family member 2B (WNT2B). Specifically, microRNA-338-5p tended to be low-expressed in NPC tissues and cell lines, compared to the non-tumor nasopharyngeal mucosa tissues and normal nasopharyngeal cell line (NP69). Upregulation of microRNA-338-5p inhibited proliferation, mobility, and epithelial-mesenchymal transition (EMT) in NPC cells in vitro, while silencing of microRNA-338-5p had opposite effects. Consistently, microRNA-338-5p suppressed tumorigenesis of NPC cells in vivo. In addition, microRNA-338-5p targeted WNT2B for degradation and inhibition, and the inhibiting effects of microRNA-338-5p overexpression on NPC development were reversed by upregulating WNT2B.

Conclusions

Taken together, we concluded that microRNA-338-5p targeted WNT2B to hinder NPC development.

Effects of isoprenylcysteine carboxylmethyltransferase silencing on the migration and invasion of tongue squamous cell carcinoma

OBJECTIVES

The effect of isoprenylcysteine carboxymethyltransferase (ICMT) silencing on the migration and invasion of tongue squamous cell carcinoma was investigated by constructing the small interfering RNA (siRNA) of ICMT.

METHODS

Through liposomal transfection, siRNA was transfected into human tongue squamous cell carcinoma CAL-27 and SCC-4 cells (ICMT-siRNA group) with a negative control group (transfected with NC-siRNA) and a blank control group (transfected with a transfection reagent but not with siRNA). Quantitative real-time polymerase chain reaction was performed to analyze the mRNA expression of ICMT and RhoA in each group of cells after transfection and to measure the silencing efficiency. Western blot was applied to examine the expression levels of ICMT, total RhoA, membrane RhoA, ROCK1, matrix metalloproteinase (MMP)-2, and MMP-9 proteins in each group. The migration and invasion abilities were evaluated via wound healing and Transwell motility assays.

RESULTS

After CAL-27 and SCC-4 cells were transfected with ICMT-siRNA, the expression levels of ICMT genes and proteins decreased significantly in the experimental group compared with those in the negative and blank control groups (P<0.05). The mRNA and total protein expression levels of RhoA in the two groups were not significantly different (P>0.05). The expression levels of RhoA membrane protein, ROCK1, MMP-2, and MMP-9 decreased (P<0.05). The migration and invasion abilities were inhibited (P<0.05).

CONCLUSIONS

The migration and invasion abilities of CAL-27 and SCC-4 cells were reduced significantly after the transfection of ICMT-siRNA, and the involved mechanism might be related to the RhoA-ROCK signaling pathway.

Beyond the Mevalonate Pathway: Control of Post-Prenylation Processing by Mutant p53

Missense mutations in the TP53 gene are among the most frequent alterations in human cancer. Consequently, many tumors show high expression of p53 point mutants, which may acquire novel activities that contribute to develop aggressive tumors. An unexpected aspect of mutant p53 function was uncovered by showing that some mutants can increase the malignant phenotype of tumor cells through alteration of the mevalonate pathway. Among metabolites generated through this pathway, isoprenoids are of particular interest, since they participate in a complex process of posttranslational modification known as prenylation. Recent evidence proposes that mutant p53 also enhances this process through transcriptional activation of ICMT, the gene encoding the methyl transferase responsible for the last step of protein prenylation. In this way, mutant p53 may act at different levels to promote prenylation of key proteins in tumorigenesis, including several members of the RAS and RHO families. Instead, wild type p53 acts in the opposite way, downregulating mevalonate pathway genes and ICMT. This oncogenic circuit also allows to establish potential connections with other metabolic pathways. The demand of acetyl-CoA for the mevalonate pathway may pose limitations in cell metabolism. Likewise, the dependence on S-adenosyl methionine for carboxymethylation, may expose cells to methionine stress. The involvement of protein prenylation in tumor progression offers a novel perspective to understand the antitumoral effects of mevalonate pathway inhibitors, such as statins, and to explore novel therapeutic strategies.